New study finds that gay men on HIV treatment don't pass the virus to sexual partners

International study of gay couples reports no transmissions from an HIV-positive partner who is undetectable on treatment

A study of 343 gay couples, where one partner had HIV and the other did not, has not found a single case of HIV transmission despite 16,889 acts of condomless anal sex.

The Opposites Attract study looked at whether HIV is transmitted between gay male couples of different HIV status when the HIV-positive partner is on treatment that fully suppresses their HIV. The HIV-positive partners in Opposites Attract had a so-called ‘undetectable viral load’ 98% of the time.



Having sex without condoms, which used to be called ‘unprotected’ or ‘unsafe’ sex. However, it is now recognised that PrEP and U=U are effective HIV prevention tools, without condoms being required. Nonethless, PrEP and U=U do not protect against other STIs. 

safer sex

Sex in which the risk of HIV and STI transmission is reduced or is minimal. Describing this as ‘safer’ rather than ‘safe’ sex reflects the fact that some safer sex practices do not completely eliminate transmission risks. In the past, ‘safer sex’ primarily referred to the use of condoms during penetrative sex, as well as being sexual in non-penetrative ways. Modern definitions should also include the use of PrEP and the HIV-positive partner having an undetectable viral load. However, some people do continue to use the term as a synonym for condom use.

Undetectable = Untransmittable (U=U)

U=U stands for Undetectable = Untransmittable. It means that when a person living with HIV is on regular treatment that lowers the amount of virus in their body to undetectable levels, there is zero risk of passing on HIV to their partners. The low level of virus is described as an undetectable viral load. 

The study recruited and followed-up gay couples at clinics in Australia, Thailand and Brazil.

The study was presented at the International AIDS Society Conference on HIV Science in Paris today. A detailed analysis of the research findings is available at

The evidence from Opposites Attract adds to the evidence from the PARTNER study that HIV-positive people on effective HIV treatment that fully suppresses their virus cannot transmit their infection through sex. Taken together, the two studies have not found a single case of HIV transmission in nearly 40,000 acts of condomless anal sex between gay men.

This new data adds further strength to the “U=U” (Undetectable equals Untransmittable) tagline of the Prevention Access Campaign, whose consensus statement has been signed by both NAM and the International AIDS Society.

Professor Andrew Grulich of the Kirby Institute and chief investigator on the study summed up the findings: “Our data add to previous studies which show that there has never been a recorded case of HIV transmission from an HIV-positive person to their HIV-negative sexual partner when the HIV-positive partner had undetectable viral load.”

NAM’s Executive Director, Matthew Hodson, commented, “In terms of HIV prevention, if condom use is safer sex, then sex with someone who has maintained an undetectable viral load is even safer sex.”

The studies also found that if the positive partner is on successful treatment, even having another sexually transmitted infection does not increase the risk of HIV being transmitted. Significant numbers of participants in both studies had a sexually transmitted infection at some point.

Sexual position also made no difference even though when viral load is not suppressed and condoms are not used, transmission is 10-20 times more likely if the HIV-positive partner is the ‘top’ rather than the ‘bottom’.

Matthew Hodson welcomed the new data. “We’ve known for many years that HIV treatment, as well as saving lives, also plays a role in reducing transmission risk. Our confidence that those of us with HIV are not a risk to our sexual partners is crucial to the transformation we have seen in HIV since the introduction of effective treatment.”

Matthew Hodson continued, “For many years, those of us with diagnosed HIV have had to live with the idea that our bodies are dangerous. This has had a profound emotional impact on many people. It is wonderful to consider what this news can mean to people with HIV who are too scared to have sex in case they pass their virus on, or to those in relationships with HIV-positive people whose sexual pleasure has been hampered by fear.

“The preventative impact of effective HIV treatment underlines the importance of expanding access to treatment and of improving treatment uptake and adherence for all people living with HIV worldwide.”

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